Regulated proteolysis is used to drive many biological processes, including the cell cycle, cell death, and embryonic patterning. It is also thought to mediate complex brain functions such as learning and memory. Not surprisingly, then, defects in regulated proteolysis lead to human pathologies such as cancer and neurodegenerative disease. The overall goal of this grant is to understand the mechanisms of regulated proteolysis involving the coordinated action of serine proteases and their inhibitors called serpins. Three specific aims are proposed: 1) To test the hypothesis that a serpin is an inhibitor of proconvertases, serine proteases that activate a wide range of cellular and pathogenic proteins, including hormones, growth factors, and virulence determinants. 2) To identity serine proteases involved in the melanization reaction, an insect analogue of the mammalian blood clotting reaction and a critical determinant of malarial resistance in the mosquito. 3) To perform an RNAi-based screen for serpin function that ultimately will lead to the identification of new biological processes involving serine proteases and serpins. These studies will exploit Drosophila, which utilizes many of the same molecular and cellular mechanisms as mammals, to learn general principles of how regulated proteolysis involving serine proteases and serpins is used for diverse biological purposes.